In recent years, in the field relative to semiconductor manufacturing equipment, a so-called “gas dividing and supplying system” has been employed in many cases with the enlargement of a process chamber, and various types of gas dividing and supplying systems have been developed. FIG. 5 shows an example of a conventional gas dividing/supplying apparatus that uses a thermal-type MFC (mass flow controller) or a pressure-type FCS (flow control system), and gas G emitted from a gas supply source S is divided and supplied to a process chamber C through the flow control devices in the ratio of a flow rate Q1 to a flow rate Q2. More specifically, FIG. 5 shows a chamber C; gas dischargers D, Dc and De; a wafer H; and a supporting device I.
By the way, in the flow control device MFC (or FCS), when gas starts to be supplied, a gas flow-in phenomenon (so-called “overshooting” phenomenon) is liable to easily occur, and, especially in the thermal-type flow control device MFC, the occurrence of the overshooting phenomenon is inevitable.
For example, based on results obtained by analyzing the cause of a fluid overshooting phenomenon that has occurred immediately after starting the supply of gas by use of a gas supplying apparatus, arranged as shown in FIG. 6, the present inventors have determined that, in a gas supplying apparatus 50 that uses the conventional mass-flow controllers, (a) most gas that causes the overshooting phenomenon is gas that stagnates in the pipe passages L1 to L3 by which changeover valves V1 to V3 are connected to mass-flow controllers MFC1 to MFC3, respectively, and (b) the structure itself of each mass-flow controller MFC1 to MFC3 increases the stagnation of gas that causes the overshooting phenomenon. In FIG. 6, reference symbol 51 designates a chamber.
In more detail, as shown in FIG. 7, which is a block diagram showing a basic structure of a conventional mass-flow controller, gas that has flowed in from the primary side is divided into gas portions flowing through a laminar flow bypass 59 and a sensor bypass 60, and the mass flow of the gas is determined by a sensor 61 in the form of temperature change in proportion thereto, and the determined temperature change is converted into electric signals in a bridge circuit 62, and the resulting electric signals are output through an amplifier circuit 63 and others to a display 64 and to a comparison control circuit 65 as linear voltage signals, respectively. Meanwhile, set signals transmitted from outside are input from a setter 66 into the comparison control circuit 65, in which the difference between the aforementioned detected signals and the set signals is calculated, and the resulting signal difference is sent into a valve drive 67, which controllably opens or closes a flow control valve 68 in a direction in which the signal difference becomes zero. In the FIG. 7, reference symbol 69 designates a power unit.
Now, if the changeover valve V1 mounted on the secondary side is suddenly closed while the mass-flow controller is in operation, the gas flowing through the sensor 61 comes to a standstill and, therefore, the control system of the mass-flow controller works transiently to increase the flow of gas, and the flow control valve 68 is opened. As a result, the gas pressure in the secondary-side line L1 rises, causing the gas to stagnate therein. Thereafter, when the changeover valve V1 is opened, the stagnating gas rushes into the chamber side through the changeover valve V1, causing the gas overshooting phenomenon.
Therefore, the occurrence of overshooting of gas in the gas dividing/supplying apparatus inevitably causes a decrease in operating efficiency of semiconductor manufacturing facilities, or a decrease in quality of products. Therefore, it is necessary to prevent the occurrence of overshooting as much as possible.
On the other hand, in recent years, in this type of gas dividing/supplying apparatus of semiconductor manufacturing equipment, a desire to reduce this apparatus in size and in cost has increased. To meet such a desire, as shown in FIG. 8, a gas dividing/supplying apparatus has been developed in which the flow of a total quantity Q of gas supplied from a gas supply source is controlled by use of a pressure-type flow control system (FCS) 4, and in which divided flow quantities Q1 to Qn of gas are controlled in divided flow passages L1 to Ln, respectively.
In FIG. 8, reference symbol 1 designates the gas supply source, reference symbol 2 designates a pressure regulator, reference symbol 3 designates a pressure sensor measuring Po, reference symbol 4 designates a pressure-type flow control system (FCS), reference symbols 5a and 5b designate pressure gauges measuring P1 and P2, respectively, reference symbol 6 designates a thermal-type mass flow sensor (MFM), reference symbol 7 designates a motor-operated valve, reference symbol 8 designates a valve drive unit, reference symbol 9 designates a vacuum pump, reference symbol 10 designates a throttle valve, reference symbol 11 designates a signal generator, reference symbol 12 designates a PID controller, reference symbol 13 designates a process chamber, reference symbol Sm designates a flow detection signal, reference symbol Sa designates a flow setting signal, and reference symbol Sv designates a valve driving signal.
In the gas dividing/supplying apparatus of FIG. 8, a total flow quantity Q of gas whose flow has been controlled by the pressure-type flow control system 4 is supplied to divided flow passages L1, L2, and Ln in divided flow quantities Q1, Q2, and Qn, respectively. In other words, divided flow quantities Q1, Q2, and Qn of gas flowing through the divided flow passages L1, L2, and Ln, respectively, are supplied to the chamber 13 in such a way that, for example, in the divided flow passage L1, the motor-operated valve 7 is subjected to feedback control by means of the controller 12 according to a flow detection signal Sm emitted from the thermal-type mass flow sensor (MFM) 6, and, as a result, the gas is controlled to have a divided flow quantity Q1 equal to a flow setting signal Sa emitted from the signal generator 11 and is supplied to the chamber 13. In FIG. 8, a divided flow control mechanism of the divided flow passages L1, L2, and Ln is omitted.
However, also in the gas dividing/supplying apparatus, a peak Smp appears in the flow detection signal Sm of the thermal-type mass flow sensor (MFM) 6, and so-called overshooting occurs in the gas having a flow quantity Q1 flowing through the divided flow passage L1 as shown in FIG. 9, for example, immediately after starting a gas admission into the divided flow passage L1 (referred to as “when gas is admitted for supply”) by inputting a flow setting signal Sa from the signal generator 11 and by starting the pressure-type flow control system (FCS) 4.
In other words, a peak flow detection signal Smp, as shown in FIG. 9, will occur in the flow detection signal Sm, and overshooting will occur in gas having a divided flow quantity Q1 if the flow setting signal Sa equivalent to a rated flow (100% Full Scale (F.S.) flow output) is input to the controller 12 at a point t0, and gas is then supplied to the thermal-type mass flow sensor (MFM) 6 at a point t1, and a flow detection signal Sm is input to the controller 12 as shown in FIG. 9.